This invention relates to an electronic system for controlling apparatus for peeling and coiling a continuous strip of metal cut from a rotating billet, and more particularly, to a system for preventing damage to the billet and cutting apparatus if the strip breaks during threading of the machine.
Machines have been built to manufacture thin metal strips by continuously feeding or moving a cutting tool at a specific rate into the peripheral surface of a rotating metal billet so as to cut and peel a continuous metal strip from the billet surface.
Various types of steels and non-ferrous alloys have been formed into billets using casting techniques and the hot isostatic pressing of powders. The properties of the material employed, the technique used in forming the billet to be peeled, and the rate and conditions of peeling all contribute to the quality of the peeled strip. Peeled strips generally have a smooth and a rough side, the former being produced by the burnishing of the strip by the cutting tool as it advances into the billet. The roughness on the side opposite the cutting tool is determined by the prior history of billet processing as well as thickness of the strip, coolants, cutting tool geometry and composition. By optimizing the conditions under which peeling is performed it is possible to produce a continuous high quality strip of metal useful in a variety of applications.
Control systems have been developed whereby the surface speed of the billet, the speed of the peeled strip and the rate of advancement of the cutting tool into the surface of the billet can be adjusted to accurately control the thickness of the strip. U.S. Pat. No. 4,274,315 discloses such a control system wherein sensors are used to monitor the thickness of the strip and correct for unwanted variations thereof. A data processor can be used to gather and process information from the various system components to maximize operating speed of the machine and the quality of the strip that is produced.
Existing machines have utilized a tension producing coiling assembly as part of the peeling process. The coiling assembly can include a motor driven rotatable spindle with a wrapping mechanism to assist in the threading of the peel onto the coiler. The rotating spindle pulls and coils the metal strip as it is peeled from the billet.
The coiling assembly has a "running" mode for normal high-speed operation of the machine during peeling and a "threading" mode. The threading mode of the coiler consists of rotating the spindle at a relatively slow speed that is coupled to the speed of billet rotation. The initial threading of the strip also involves clamping the leading edge of the strip to the mandrel of the coiler assembly. However, the initially peeled strip material can be distorted due to the absence of tension. This distorted material is usually sheared and discarded before wrapping of the strip. Systems have been developed for shearing and wrapping the strip onto the mandrel during threading.
Threading is a critical step of the peeling process in which the initial portion of material that is cut from the billet is wrapped onto the coiler. A number of systems have been developed for the purpose of performing this initial wrap. For example, U.S. Pat. No. 4,389,868 describes such a belt wrapper assembly.
The initial portion of the strip is not under any applied tensile force. Consequently, the shape of the initial strip is poor and may be difficult to wrap on the coiler without producing a non-circular coil of strip. Also, when the strip is not under tension, greater shear deformation may occur at the cutting tool. This produces an initial strip that is thicker than strip under tension and may be more heavily cold worked to produce a brittle material that can break and disrupt the threading process.
During the threading of the peeling machine the cutting tool is advanced into the billet to maintain a predetermined thickness of the peeled strip. The coiler can be operated during threading at a constant speed relative to the spindle or in a constant tension mode. Thus, if the strip were to break during threading, many existing machines would continue to advance the tool into the billet before the operator could shut down the machine and initiate re-threading.
Peeling machines which couple the speed of the take-up coiler to the speed at which the tool advances into the billet during threading can result in damage to the billet, the tool and the hydrostatic spindle, if the strip breaks during threading. The coiler, no longer acting under the tension of the strip when it breaks, accelerates to a higher speed thereby causing the tool to dive into the billet.